The existence in brain, sympathetic ganglia and adrenal medulla of multiple forms of peptides that cross-react with antibodies specific for enkephalin has been demonstrated. These enkephalin-like peptides are particularly abundant in adrenal glands where they also exhibit a considerable amount of molecular heterogeneity. One of the newly detected enkephalin-like peptides from caudate is biologically active in inhibiting the electrically induced contraction of guinea pig ileum and causing catatonia when injected intraventricularly. These effects are naloxone-resistant indicating that they act on receptors different from those involved in the anti-nociceptive action of morphine. A similar enkephalin-like peptide also exists in adrenal medulla. This novel enkephalin-like peptide may play an important role in the adrenal function since it is a major component of the total low molecular weight enkephalin-like peptides.